Update config.yml with Zulip

Author: joshmoore

.github/ISSUE_TEMPLATE/config.yml

@@ -3,8 +3,8 @@ contact_links:
   - name: ✨ Propose a new major feature
     url: https://github.com/zarr-developers/zarr-specs
     about: A new major feature should be discussed in the Zarr specifications repository.
-  - name: ❓ Discuss something on gitter
-    url: https://gitter.im/zarr-developers/community
+  - name: ❓ Discuss something on Zulip
+    url: https://ossci.zulipchat.com/
     about: For questions like "How do I do X with Zarr?", you can move to our Gitter channel.
   - name: ❓ Discuss something on GitHub Discussions
     url: https://github.com/zarr-developers/zarr-python/discussions